Ground-engaging tools such as furrow openers and cultivating tools are well known for mounting on an implement frame for use in agricultural field operations. It is a main objective of such implements to have the ground-engaging tools of the implement extend the same distance into the ground across the width of the implement so that the soil is worked at an even depth across the whole field.
While the working depth is important for all ground working implements, it is particularly important for furrow openers on seeding and fertilizing implements where the depth and placement of seed and fertilizer can affect the yield of the seeded crop.
Such ground-engaging tools are typically mounted on an arm or shank that is attached to the implement frame. In one configuration the arm extends rearward and is pivotally mounted to the frame. A ground following depth wheel is placed at the end of the arm and a spring or similar bias element exerts a downward force on the arm to maintain the depth wheel in contact with the ground. The furrow opener extends downward just ahead of the depth wheel, and the furrow opener is maintained at a substantially constant depth by the depth wheel which can move up and down with respect to the frame as ground contours vary. In such a configuration, the height of the implement frame above the ground should also be maintained substantially constant as well since the working depth of the furrow opener depends on both the height above the ground of the front end of the arm, attached to the frame, and the height above the ground at the rear end, attached to the wheel. Mounting the furrow opener as near to the depth wheel as possible, however, reduces the effect of the front end height, and maximizes the depth control provided by the depth wheel.
Such a ground following configuration is disclosed in U.S. Pat. No. 5,752,454 to Barton where the furrow opener is a disc type furrow opener, and U.S. Pat. No. 5,396,851 to Beaujot where the furrow opener is a hoe type furrow opener. In narrow configurations the hoe-type opener is often referred to as a knife opener. Both types of furrow openers are commonly used in agriculture. Such individual ground following furrow openers provide somewhat improved depth control but are relatively complex and costly and require considerable maintenance. Each furrow opener must also be adjusted individually to change the furrow depth, requiring considerable time and often substantial effort as well, depending on the adjusting mechanism.
In a more common configuration, the ground-engaging tools are mounted to the implement frame at a fixed working distance below the frame such that the working depth of the ground-engaging tools is determined solely by the tool's distance below the frame. The frame is mounted on ground following frame wheels and leveled such that the frame is substantially the same height above the ground across its width as it moves along the field. The tools then work the ground at an even depth. To vary the working depth, or to disengage the tools from the ground, the frame wheels are raised or lowered with respect to the frame, thereby varying the distance between the frame and the ground. Thus in this configuration the ground working or furrow depth is more readily adjusted as individual adjustment of each tool or furrow opener is not required.
In this fixed configuration, the ground-engaging tools are typically mounted at the lower end of an arm or shank that has an upper end thereof attached to the frame. In this fixed configuration, the arm is also typically pivotally attached to the frame as in the ground following configuration with a depth wheel as described above. In this fixed configuration, however, the pivotal attachment is only provided so that the ground-engaging tool may move upward from a normal working position to clear obstacles, such as rocks or the like, that may be encountered in the field. Such a fixed configuration is disclosed in U.S. Pat. No. 6,237,697 to Butterfield et al.
In the working position, the arm is maintained at a fixed downward location by a heavy bias force that maintains the downward location in normal soil conditions until an obstacle is encountered that exerts a sufficient force on the arm to overcome the bias force and move back and up to clear the obstacle. Once the obstacle is cleared, the arm is again forced down to the working position. It is also known to provide implements with the fixed configuration wherein the arm is rigidly fixed to the frame and there is no provision for clearing obstacles.
The Butterfield '697 patent also discloses a typical adjustable mechanism for mounting the upper end of the arm to an implement frame such that the distance between the furrow opener and the frame can be adjusted. Such an adjustment allows for some chosen furrow openers to be lower or higher than others to compensate for furrow opener wear, working in hard packed wheel tracks, and such other anomalies as are found across the width of a seeding implement.
Furrow openers must be maintained at a constant and correct orientation with respect to the operating travel direction in order to cut a satisfactory furrow. Openers with a hoe-type ground-engaging element for example are generally oriented at an operating angle of zero, while typical disc-type openers are oriented at an angle of between 4 and 12 degrees. Especially when the furrow opener is working in the relatively hard un-tilled soil of a no-till seeding operation, the ground-engaging element can encounter considerable forces which tend to move the element out of the proper orientation. As an example, a typical disc furrow opener for use in no-till seeding can be oriented at a small angle of approximately 4 degrees with a preferred tolerance of 0.5 degrees. An apparatus for mounting this furrow opener must then provide considerable strength to maintain that tolerance in hard soil.
In order to maintain this orientation conventional implements typically employ members with a square or rectangular cross section that are mated and clamped to provide engagement that will hold the furrow opener rigid and resist twisting out of the desired orientation. Such a typical mechanism is illustrated in Butterfield '697, where once the arm is moved to the desired vertical position, bolts are placed through appropriate holes and tightened so that the arm flanges with the mounting holes are clamped to the frame mounting member.
Clamping is required to keep the furrow opener rigid with respect to the frame to maintain the proper operating angle on the opener. Using commercially economical manufacturing processes, the sliding fit between the flanges and the frame mounting member is not sufficiently close to maintain the angle within the required tolerances.
U.S. Pat. No. 4,909,335 to Walt, Jr. discloses a mechanism for adjusting the vertical position of a ground-engaging tool with respect to an implement frame. The mechanism comprises a square tube attached to a cultivating tool that slides inside another square tube that is attached to the implement frame. A screw is operative to move the inside tube up and down with respect to the outer tube in order to adjust the vertical position of the ground-engaging tool with respect to the frame.
In Walt, Jr., the implement is a cultivating implement wherein precise orientation with respect to the operating travel direction is not as critical as it is with furrow openers that deposit seed, and in particular disc type furrow openers wherein the angle of the disc with respect to the operating travel direction must be maintained within a tight tolerance to provide satisfactory furrow forming and seed placement. While the tubes in the apparatus of Walt could be manufactured to sufficient precision to provide the required degree of precision to maintain a furrow opener at the required angle, such tubes are not commercially available but must be specially manufactured at significant cost. Thus a slidable adjustment mechanism such as disclosed in Walt, Jr. is not economically viable for furrow openers.
Cylindrical shafts with a circular cross section are manufactured with considerable precision and are commercially available at a reasonable cost. Such cylindrical shafts are much more easily made to precise specifications since they can be turned on a lathe or the like. Such cylindrical shafts are mass-produced for use in hydraulic cylinders, and are also chrome plated to resist corrosion, and so are available at reasonable cost. Similarly corresponding cylindrical bores are readily made in brackets or the like so that the shaft can be slidably received in the bore with very close tolerances, such as would provide for the precision control of furrow openers.
Such cylindrical shafts alone however cannot resist twisting since they will rotate as well as slide in the bore unless a groove or keyway, and corresponding key are provided. Considerable twisting forces can be exerted on furrow openers, such that a large diameter shaft and large keyway and key would need to be provided to maintain a furrow opener at the desired orientation under field conditions. The bracket with the bore must be sized and shaped accordingly as well. The resulting adjustment mechanism would be costly, and not likely economical for use in agricultural implements.